In mobile wireless communications systems user terminals (e.g., mobile phones) are able to move. This means that communication requirements will vary from time to time and from place to place, and also that the communication channel over which information is sent will vary in quality over time. Various techniques have been designed to allow for efficient use of the physical air interface when this occurs, including (but not limited to) handover (where the wireless link is changed from one base site to another), macrodiversity (where a link is maintained with two or more base sites at the same time), Dynamic Channel Allocation (DCA) where the air interface resources available to different base sites are pooled and shared out between the sites dynamically depending on current demand, Link Adaptation (where the channel coding is changed in response to the channel quality) Adaptive Modulation (where the modulation is changed in response to the channel quality) and Adaptive Power Control (APC) where the transmission power is changed in response to the channel quality. These different techniques all trade resource on the air interface against quality of the user data stream (the user Quality of Service), and therefore have to be controlled in a coordinated manner. However, efficient control of a system with so many variables is very difficult.
The generic definition of Quality of Service (QoS) is “The collective effect of service performances which determine the degree of satisfaction of a user of the service”. The satisfaction of the user depends significantly on the service being considered. For example, QoS measures for speech would include clipping (loss of the start of speech bursts), echoes, crosstalk, distortion, acoustic noise, quantisation noise, and overall signal to noise ratio. For a video service, the QoS parameters would include block distortion, blurring, edge busyness (distortion concentrated at the edge of objects, like edges shimmering), jerkiness, tiling or pixelation, frame freezing, or colour cycling (where colour stability is lost, and colours cycle through a range of hues).
While there are a large number of different QoS measures which are service dependent, it is possible at the transmission level of the system to map these different measures to generic QoS measures related to the network capabilities. These QoS measures are:                bit rate, both in terms of mean bit rate (throughput) and variation of bit rate (burstiness);        delay, both in terms of absolute delay (network transit delay) and delay variation (jitter);        data corruption, in terms of Bit Error Rate (BER) and Frame Erasure Rate (FER) (where packets are lost or dropped rather than received with error).        